Numerical Analysis On Lateral Floating Characteristics Of A Helicopter With Emergency Floatation Bags

One of the main causes of the helicopters' ditching accidents is the sinking and rollover caused by their own floating characteristics.Nowadays,the helicopters have had enough floating capacity by equipping with air bags at home and abroad.However,at present,few people study the anti-rollover capability of helicopters with numerical analysis on the basis of considering the airbag flexibility.Therefore,it is very important to establish a calculation scheme for the lateral floatation characteristics of helicopters on the premise of the airbag flexibility.Firstly,the theory of central difference method and the traditional theory of ship's floating state and stability are introduced.Combining with the finite element method,the static stability calculation methods of helicopter without considering the flexibility of airbag and connecting belt and considering the flexibility of airbag and connecting belt are established respectively.The pressure formula of stability equation based on finite element is deduced and the theoretical analysis is carried out.Secondly,the finite element model of a helicopter is established,and the static stability calculation of the helicopter is realized by using MATLAB programming and Ls-dyna simulation.The reliability of the calculation method is verified by comparing the calculation results with the literature and experimental results.The influence of the front and rear limits of the gravity center on the static stability is studied;the influence of different internal pressure of the airbag on the static stability is studied,and the bigger and straighter the internal pressure of the airbag is obtained.The conclusion that the better the static stability of the lift is,it is consistent with the theory.After that,a five-stage regular wave is built to simulate the roll of a complete helicopter under the action of wind and wave.The calculation shows that the helicopter configuration with flexible airbag has excellent floating ability under the five-stage regular wave.A three-stage wave is built and the roll response curve of the helicopter is obtained.The influence of the same sea condition on the roll response also provides a basis for the accuracy of the prediction results of the roll response.Finally,the single-degree-of-freedom dynamic equation of helicopter rolling response under wind and wave is established.By Runge-Kutta iteration method and using the software of matlab,the static stability curve of helicopter and rolling response curve under five-stage sea state regular wave are obtained,and the response prediction under arbitrary irregular wave is realized.